Since the last decade, metal nanoparticles have been considerably explored for the treatment of several diseases such as cancer, cardiovascular related diseases, diabetes, Parkinson's, arthritis, HIV, hepatitis, tuberculosis, Alzheimer's, cirrhosis etc due to their unique fundamental physical and chemical properties (Alivisatos, P. et al, Nat. Biotechnol. 2004; 22: 47-52; Boisselier, E. et al. Chem. Soc. Rev. 2009; 38: 1759-1782; Gao, X. et al. Nat. Biotechnol. 2004; 22: 969-976; Kumar, A. et al. Nat. Mater. 2008; 7: 236-241; Mulder, W. J. M. et al. Arterioscl. Throm. Vas. 2008; 28: 801-802; Patra, C. R. et al. Adv. Mater. 2008; 20: 753-756; Patra, C. R. et al. Cancer research, 2008; 68: 1970-1978; Patra, C. R. et al. Nano Lett. 2011; 11: 4932-4938; Shankar, S. S. et al. Nat. Mater. 2004; 3: 482-488; Sung, H. W. et al. Nanomedicine-Uk, 2011; 6: 1297-1300; Wei, P. F. et al. Biomaterials, 2014; 35: 899-907). Recently scientists have discovered new classes of nanoparticles i.e. metal complex nanoparticles such as Prussian blue nanoparticles (PBNPs) and its analogs (Collins, A. M. et al. Nanoscale, 2010; 2: 2370-2372; De la Escosura, A. et al. Chem. Comm. 2008; 1542-1544; Dominguez-Vera, J. M. et al. Inorganic chemistry, 2003; 42: 6983-6985; Dumont, M. F. et al. Int. J. Nanomedicine, 2014; 9: 2581-2595; Fiorito, P. A. et al. Chem. Comm. 2005; 366-368; Fu, G. et al. Chem. Comm. 2012; 48: 11567-11569; Hornok, V. et al. J. Colloid Interface Sci. 2007; 309: 176-182; Hu, M. et al. Angew Chem. Int. Ed. Engl. 2012; 51: 984-988; Uemura, T. et al. J. Am. Chem. Soc. 2003; 125: 7814-7815; Wang, H. et al. J. Hazard. Mater. 2011. 191, 163-169; Ye, S. et al. Chem. Comm. 2011; 47: 6831-6833) (Kawamoto et al. EP2116511 A1, 2009; Kawamoto et al. US7678188 B2, 2010; Kawamoto et al. U.S. Pat. No. 8,349,221 B2, 2013). Incorporation of metals in the co-ordination complexes change their properties that could be useful for chelating agent for heavy metal toxicity, coating medium, drug delivery vehicles, MRI substance, luminescent materials, sensors etc. (Dumont, M. F. et al. Int. J. Nanomedicine, 2014; 9: 2581-2595; Fiorito, P. A. et al. Chem. Comm. 2005; 366-368; Fu, G. et al. Chem. Comm. 2012; 48: 11567-11569; Ye, S. et al. Chem. Comm. 2011; 47: 6831-6833). Prussian blue complex has gained huge interests to remove the heavy metals and radioactive elements due to its chelating property (Stevens, W. et al. Therapy and toxicology, 1974; 10: 1-22; Thompson, D. F. et al. The Annals of pharmacotherapy, 2004; 38: 1509-1514). Because of the biocompatibility nature, PBNPs have been utilized for several theranostics applications like drug delivery, MRI imaging etc. (Jing, L. et al. Biomaterials, 2014; 35: 5814-5821; Lian, H. Y. et al. Chem. Comm. 2012; 48: 5151-5153; Schleich, N. et al. Int. J Pharm. 2013; 447: 94-101). However, potential biomedical applications of Prussian blue analogs have not been extensively explored for cancer therapeutics and antibacterial activity study. In this context, we have designed and developed polymer stabilized silver Prussian blue analogue, Ag3[Fe(CN)6] that exhibit itself as potential anticancer as well as anti-bacterial agent without external source of anti-cancer drugs or antibiotics. The present invention discloses an improved synthesis of highly stable silver Prussian blue nanoparticles (SPB-NPs) and its therapeutic applications towards anticancer and antibacterial activities. Additionally, the detailed mechanistic studies for the anticancer and antibacterial activities have been discussed. The present invention described the simple improved method for the synthesis biocompatible SPB-NPs would be potentially useful for the development towards alternative anti-cancer agent as well as anti-bacterial agent in near future.